In a typical consumable electrode arc welding, welding is performed by feeding a welding wire as a consumable electrode at a constant feeding rate and generating an arc between the welding wire and base material. In the consumable electrode arc welding, both the welding wire and the base material are mostly placed in a welding state in which a short circuit state and an arc generation state are alternately repeated.
In order to further improve welding quality, there has been proposed a method of performing welding by alternating feeding of a welding wire between forward feeding and reverse feeding cyclically (see Patent Document 1, for example). Further there has been proposed a constriction detection control method in which a generation amount of spatter is reduced by rapidly reducing a welding current in response to detection of a constriction of a droplet, as a precursory phenomenon of arc regeneration, and regenerating an arc in a small current-value state (see Patent Document 2, for example). Hereinafter these welding methods will be explained.
FIG. 4 is a waveform diagram of the welding method in which the forward feeding period and the reverse feeding period are alternated cyclically as to the feeding rate of the welding wire and also constriction detection control is performed. (A) of this figure shows a waveform of a feeding rate Fw, (B) of this figure shows a waveform of a welding current Iw and (C) of this figure shows a waveform of a welding voltage Vw, Hereinafter explanation will be made with reference to this figure.
As shown in (A) of this figure, in the feeding rate Fw, an upper side and a lower side than 0 represent a forward feeding period and a reverse feeding period, respectively. The forward feeding represents feeding of the welding wire in a direction approaching the base material, whilst the reverse feeding represents feeding of the welding wire in a direction separating from the base material. The feeding rate Fw has a waveform which changes sinusoid ally and shifts on the forward feeding side. Thus as an average value of the feeding rate Fw is positive, the welding wire is fed forwardly in average.
As shown in (A) of this figure, the feeding rate Fw is 0 at a time t1. A period from the time t1 to a time t2 corresponds to a forward feeding acceleration period. The feeding rate is the maximum value of the forward feeding at the time t2. A period from the time t2 to a time t3 corresponds to a forward feeding deceleration period. The feeding rate is 0 at the time t3. A period from the time t3 to a time t4 corresponds to a reverse feeding acceleration period. The feeding rate is the maximum value of the reverse feeding at the time t4. A period from the time t4 to a time t5 corresponds to a reverse feeding deceleration period. The feeding rate Fw changes repeatedly with a single cycle from the time t1 to the time t5.
Short circuit between the welding wire and the base material occurs mostly before or after the maximum value of the forward feeding at the time t2. This figure shows a case where the short circuit occurs at a time t21 during the forward feeding deceleration period after the maximum value of the forward feeding. If the short circuit occurs at the time t21, the welding voltage Vw reduces rapidly to a short-circuit voltage value of a few volts as shown in (C) of this figure, and the welding current Iw also reduces to an initial current value of a small current value as shown in (B) of this figure. Thereafter the welding current Iw increases with a predetermined inclination. When the welding current reaches a predetermined peak value, the welding current is maintained at this value.
As shown in (A) of this figure, from the time t3, as the feeding rate Fw is placed in the reverse feeding period, the welding wire is fed reversely. The short circuit is released by this reverse feeding, and an arc is regenerated at a time t31. The arc is regenerated mostly before or after the maximum value of the reverse feeding at the time t4. This figure shows a case where the arc is generated at the time t31 during the reverse feeding acceleration period before the maximum value of the reverse feeding.
If the arc is regenerated at the time t31, the welding voltage Vw increases rapidly to an arc voltage value of several tens of volts as shown in (C) of this figure. As shown in (B) of this figure, according to detection control of a constriction of a droplet as a precursory phenomenon of arc regeneration, the welding current Iw rapidly reduces from a time earlier than the time t31 by several hundreds of μs and becomes a small current value at the arc regeneration time t31. In this respect, if a constriction is formed at the droplet, as a current path becomes narrow, a resistance value or the welding voltage value between the welding wire and the base material increases. The constriction is detected by detecting this voltage increase.
As shown in (A) of this figure, from the time t31 to the time t5, the feeding rate Fw is placed in a reverse feeding state. An arc length becomes long during this period. As shown in (B) of this figure, during the period from the time t31 to the time 15, the welding current Iw increases with a predetermined inclination, then reaches a predetermined first welding current value and maintains this value until a predetermined period elapses after the arc regeneration (time t31). Thereafter a second welding current smaller than the first welding current flows until a time 61 at which the next short circuit occurs.
As shown in (A) of this figure, the feeding rate Fw is placed in the forward feeding period from the time t5 and reaches a forward feeding peak value at a time t6. Then the next short circuit occurs at a time t61. During a period from the time t5 to the time t61, the welding voltage Vw reduces gradually as shown in (C) of this figure, and the welding current Iw also reduces gradually as shown in (B) of this figure.
As described above, a cycle of the short circuit and the arc is substantially the same as a cycle of the forward feeding and the reverse feeding as to the feeding rate. That is, according to this welding method, the cycle of short circuit and arc can be set to a desired value by suitably setting the cycle of forward feeding and reverse feeding as to the feeding rate. Thus if this welding method is implemented, the cycle of short circuit and arc can be suppressed in its variance and made substantially constant. Consequently, in combination with the constriction detection control, the welding can be performed with a small generation amount of the spatter and with good bead appearance.